DE102016220707A1 - Filter and method of making a filter - Google Patents

Abstract

The invention relates to a filter for purifying exhaust gases of an internal combustion engine with a housing through which exhaust gas can flow in the axial direction with an inflow side and with an outflow side, wherein in the housing of a plurality of filter layers, a filter body is formed, which of the exhaust gas flowable through the housing can be flowed through, wherein the filter layers (2, 16) are annular and are arranged concentrically to each other, wherein alternately two radially adjacent mutually adjacent filter layers (2, 16) are fluid-tightly connected to each other on the inflow side and two adjacent to each other in the radial direction filter layers ( 2, 16) are connected to each other at the outflow side. Moreover, the invention relates to a method for producing a filter.

Description

Technical area

The invention relates to a filter for purifying exhaust gases of an internal combustion engine with a housing through which exhaust gas can flow in the axial direction with an inflow side and with an outflow side, wherein in the housing of a plurality of filter layers, a filter body is formed, which of the flowing through the housing exhaust gas can be flowed through. Moreover, the invention relates to a method for producing a filter.

State of the art

In addition to the gaseous constituents, the exhaust gases of internal combustion engines also contain solids which flow as particles with the exhaust gas. These particles, if they are not subjected to a suitable aftertreatment, escape into the environment with the exhaust gas and can lead to contamination and chemical stress there. In particular, sufficiently small particles, which are partially respirable, can lead to health problems for humans.

In order to prevent the escape of these particles in the environment suitable filters must be provided in the exhaust system. Filters of this type are known in many variants in the prior art. These are essentially designed and designed for use in exhaust gas lines of diesel engines. As gas aftertreatment in gasoline engines will become increasingly important in the future, it is necessary to provide filters for the exhaust gas of gasoline engines, in particular direct injection gasoline engines, which are adapted to the higher temperature levels and differing pressures of the exhaust gas. Furthermore, the filters must be matched to the particle sizes that occur especially when burning gasoline.

Presentation of the invention, object, solution, advantages

Therefore, it is the object of the present invention to provide a filter which allows the filtering of particles in the exhaust gas of a gasoline-powered internal combustion engine. The filter should in particular have a compact and robust design and can be adapted with simple means for use in exhaust lines with different cable cross-sections. In this case, the filter should have a high volume-specific surface and generate the lowest possible back pressure at a simultaneously high deposition rate. Furthermore, it is the object to provide a method for producing a filter.

The object with regard to the filter is achieved by a filter having the features of claim 1.

An embodiment of the invention relates to a filter for cleaning exhaust gases of an internal combustion engine with a flow-through of exhaust gas in the axial direction housing with an inflow side and with an outflow side, wherein in the housing of a plurality of filter layers, a filter body is formed, of which by the housing flowable exhaust gas is flowed through, wherein the filter layers are annular and are arranged concentrically with each other, wherein two alternately radially adjacent filter layers are fluid-tightly connected to each other at the inflow side and two radially adjacent to each other adjacent filter layers are connected to each other on the outflow side.

The filter body as a whole is constructed such that exhaust gas can flow from the inflow side into the flow channels formed between the concentrically arranged filter layers. The exhaust gas flows in this case along an axial direction in the flow channels. However, due to the design, the flow channels are closed towards the outflow side, as a result of which the exhaust gas undergoes a deflection in the radial direction. The filter layers are designed such that the exhaust gas can flow through them, but particles of a certain defined minimum size are retained by the filter layers. The exhaust gas can thus flow through the radial deflection in the respective adjacent flow channels, which extend from the inflow side to the outflow side. After the transition into the radially adjacent flow channel arranged, the exhaust gas can flow in the axial direction to the outflow side and finally flow out of the filter body.

The fluid-tight connection of the respective filter layers on the inflow side and the outflow side avoids direct flow in the axial direction.

It is particularly advantageous if the filter body alternately has flow channels tapering in the radial direction from the inflow side to the outflow side and flow channels tapering from the outflow side to the inflow side. This is advantageous in order to allow the simplest possible inflow and outflow into the filter body or from the filter body. Due to the larger on the inflow side and the outflow side opening cross section of the flow channels, the inflow is facilitated. Due to the tapering of the flow channels from the inflow side to the outflow side, the flow-through cross-sectional area decreases whereby the transition of the exhaust gas is promoted by the filter layer in the respective adjacent flow channels. The flow channels then widening towards the outflow side lead to a simplified outflow of the exhaust gas after passing through the filter layers.

It is also advantageous if the filter body has a wavy shape in a section along the central axis of the housing, wherein the corrugation extends between the inflow side and the outflow side. This wave-shaped shape ensures that the cross-sectional area of the flow channels on the inlet side and the outlet side are as large as possible, whereby the inflow and outflow are simplified. As a result of the cross-section of the flow channels which first becomes smaller in the direction of flow, the passage of the exhaust gas is forced through the filter layer spatially delimiting the flow channel.

Essential influencing factors for the flow through the filter body are the amount of exhaust gas in the flow channel, the flow velocity and the pressure loss caused by the flow through the filter layer. Due to the first tapered flow channels and extending after passing through the filter layer flow channels a particularly advantageous design is realized, which favors the flow through the filter layers, whereby a total of a small pressure loss caused by the filter body and the cleaning rate is particularly high.

A preferred embodiment is characterized in that the filter layers are formed by a metal fleece. A metal fleece, for example, by the sintering of flat distributed metal filaments to produce. A metal fleece has the advantage that it is particularly temperature-resistant, which is particularly useful for use in gasoline-powered internal combustion engines. Furthermore, such a metal fleece can be easily adjusted to the particular required pore size. In addition, it is particularly easy to mechanically deform, which in particular simplifies the production.

It is also preferable if the filter layers have a fluid-impermeable metal strip extending in the circumferential direction on the end regions facing the inflow side and / or on the end regions facing the outflow side.

Such a metal strip is particularly advantageous in order to solder the filter layers together or welded or otherwise connect. Furthermore, it contributes to increasing the stability of the individual filter layers.

Moreover, it is advantageous if the individual filter layers are formed by annularly rolled-up metal foils, wherein the cross section of the respective filter layers tapers conically from the inflow side to the outflow side or widens conically. By means of these annularly rolled-up filter layers, which taper in each case from the inflow side to the outflow side or from the outflow side to the inflow side, the flow channels can be produced particularly advantageously with their cross-sections tapering along the flow direction and widening after passing through the filter layer.

Furthermore, it is advantageous if in each case two directly adjacent to one another in the radial direction filter layers on the inflow side or the outflow side are connected to each other in a fluid-tight manner. This is particularly advantageous in order to prevent exhaust gas from flowing unfiltered at the joint between two filter layers.

It is also expedient if the fluid-tightly interconnected filter layers are inserted into channel-like rings at the ends and the respective end regions of the filter layers are covered by the channel-like rings. In particular, the joint between the two filter layers is covered by the groove-like ring. The trough-like ring may for example also have a V-shaped cross-section, so that the metal strips of the filter layers, which are employed at a defined angle to each other, fit snugly in the ring.

In the trough-like ring advantageously also a solder material may be filled, which can be used for soldering the two respectively inserted filter layers.

Moreover, it is advantageous if a sealing element extending in the circumferential direction is arranged between two filter layers connected to one another in a fluid-tight manner. A sealing element is advantageous in order to avoid the unwanted flow through the joint. The sealing element may be formed for example by an additional metal band. Also, the sealing element can advantageously be formed by a metal strip, which partially consists of a solder material, which liquefies at the temperatures necessary for a soldering process and fluidly connects the two filter layers together during cooling.

Furthermore, it is expedient if the radially outermost first filter layer is connected at the inflow side to the housing in a fluid-tight manner in the circumferential direction and this first filter layer is fluid-tightly connected on the outflow side with the radially adjacent to the center directly adjacent second filter layer in the circumferential direction, and the second filter layer on the inflow side is fluid-tightly connected in the circumferential direction with the third filter layer in the circumferential direction, wherein this connection principle continues up to the innermost filter layer considered in the radial direction, which is closed at the end on the inflow side or the outflow side fluid-tight with itself.

This principle of the connection of the filter layers with each other leads to a filter body, each of which has tapered flow channels from the inflow side toward the outflow side, while the flow channels, which can be traversed only after passing through a filter layer, expand from the inflow side to the outflow side. Overall, this results in a particularly good to be flowed through filter body, on the one hand has a high cleaning effect, since all the exhaust gas must flow through the filter mandatory, and on the other hand generates a low pressure loss.

It is also preferable if a wave-shaped spacer element extending in the circumferential direction is arranged between two filter layers directly adjacent to one another in the radial direction. Such a spacer element can be formed for example by a corrugated ring, which extends from the inflow side or the outflow side of a few millimeters into the filter body. Preferably, the spacer element does not extend further into the filter body than does the fluid-impermeable metal strip formed on the filter layers. In this way it is ensured that no filter surface is covered by the spacer element.

Moreover, it is advantageous if the radially innermost filter layer towards the inflow side or towards the outflow side is closed at the ends in a fluid-tight manner, whereby this filter layer has a conical basic shape. This is necessary to prevent the unfiltered overflow of exhaust gas in the center of the filter body.

Furthermore, it is advantageous if the annular filter layers have a corrugation extending in the circumferential direction of the filter body. A corrugation is advantageous in order to increase the stability of the individual filter layers, as a result of which the entire filter body becomes more stable overall. In addition, as a result of the corrugation, in particular the surface of the filter layer which spatially delimits a respective flow channel is increased in comparison to a non-corrugated ring.

The corrugation is preferably designed such that they form the wave crests and the troughs in the radial direction from the otherwise annular filter layer. By a corrugation of the filter layers, in particular an enlargement of the filter surface can be achieved. The corrugation preferably enlarges the filter surface of the otherwise annular filter layers by a factor of 1.2 to 4. Particularly preferably, the filter surface is increased by a factor of 1.5 to 3.

It is also expedient for the filter layers, which are adjacent to one another in the radial direction, to have the same number of wave crests and wave troughs in the circumferential direction, with the exception of the outermost filter layer in the radial direction and the innermost filter layer. This is advantageous in order to better connect the mutually adjacent filter layers together. In particular, between the respective areas of two filter layers to be joined together, the smallest possible differences in terms of shaping and dimensions should exist in order to enable as tension-free and dimensionally stable a connection as possible. By application in an exhaust line of an internal combustion engine is to be expected with increased mechanical and thermal loads, each of which may cause damage to a joint, especially if the joint is under mechanical stress.

In order to further reduce or completely avoid stresses in the connection of two filter layers, the circumferences of directly adjacent filter layers are advantageously the same, at least in the region of the connection points.

Moreover, it is advantageous if the amplitude of the wave crests and the troughs on the filter layers in the radial direction of the filter body increases from the outside inwards. This results from the fact that the filter layers preferably all have the same number of wave crests and troughs. By naturally decreasing diameter in the radial direction, the amplitudes of the wave crests and troughs must increase.

The object with regard to the method is achieved by a method having the features of claim 16.

An embodiment of the invention relates to a method for producing a filter, wherein the filter body is formed of a plurality of filter layers, which are arranged concentrically to each other and are inserted into a housing, wherein the individual filter layers are formed by the annular winding of a metal foil and the annular Metal foils are then pulled over a conically widening form element, wherein the filter layers forming the filter body from the inside to the outside in each case by a defined distance on the conically widening form element be pulled to get conical filter layers with increasing diameter.

Preferably, a filter body is only produced from filter layers of one size. The filter layer in the filter body with the smallest cross-section thus essentially determines the size of the filter layers in the initial state. By pulling the annular filter layers over a conically widening shaped element, the annular filter layers can be widened. Depending on how far an annular filter element is pulled over the mold element, it is expanded and also receives a conical shape. If a corrugated annular filter layer is pulled over the conical shaped body or cone, the corrugation height of the individual filter layer is more or less reduced during expansion depending on how far the corrugated ring is pulled over the cone. If the annular filter layer is pulled to the end of the cone, the corrugation height is maximally reduced.

In this way, filter layers are to produce up to a certain maximum diameter. The producible maximum diameter is in particular dependent on the material properties of the filter layer. It is by this method particularly easy to obtain from uniform starting products, the individual filter layers with different diameters and a conical shape.

It is also advantageous if the annular filter layers have a corrugated shape in the circumferential direction, whereby the amplitude of the corrugation is reduced all the more by the widening of the annular filter layers on the former, the farther the filter layer is pulled over the former. By pulling the annular filter layers over the conical shaped element, the filter layer is widened. Due to the conical shape of the mold element, this happens more at one of the axial end portions than at the respective other axial end portion.

Moreover, it is advantageous if the tapered filter layers are interlocked such that the directly adjacent to each other in the radial direction filter layers are arranged alternately with the smaller cross-sectional area to the inflow and outflow, so that there is a concertina-like structure of the filter body, wherein the decreases in average cross section of the filter layers in the radial direction from outside to inside. By such an arrangement of the individual filter layer to each other a filter body with the structure according to the invention is particularly easy to produce.

Advantageous developments of the present invention are described in the subclaims and in the following description of the figures.

list of figures

• 1 eine schematische Ansicht der Einströmseite des Filterkörpers,
• 2 eine Schnittansicht durch die Stoßstelle zweier Filterlagen,
• 3 eine perspektivische Ansicht einer ringförmigen Filterlage, die aus einem gewellten Metallvlies mit endseitigen Metallbändern gebildet ist,
• 4 eine Ansicht einer ringförmigen Filterlage, wie in 3, wobei die Filterlage über ein sich konisch erweiterndes Formelement gezogen ist,
• 5 im linken Teil eine Prinzipskizze, welche zwei Filterlagen zeigt, die in einen rinnenförmigen Ring eingesteckt sind und im rechten Teil einen rinnenförmigen Ring, der eine Wellung in Umfangsrichtung aufweist, die der Wellung der ringförmigen Filterlagen angepasst ist,
• 6 eine Ansicht einer sogenannten Filtertüte, die aus einer Filterlage gebildet ist und die in radialer Richtung innerste Filterlage des Filterkörpers bildet, und
• 7 zeigt einen Schnitt entlang der Mittelachse durch das Gehäuse des Filters, wobei die einzelnen konzentrisch zueinander angeordneten Filterlagen ebenfalls im Schnitt dargestellt sind.

In the following the invention will be explained in detail by means of embodiments with reference to the drawings. In the drawings show:

• 1 a schematic view of the inflow side of the filter body,
• 2 a sectional view through the joint of two filter layers,
• 3 a perspective view of an annular filter layer, which is formed from a corrugated metal fleece with end-side metal bands,
• 4 a view of an annular filter layer, as in 3 in which the filter layer is pulled over a conically widening form element,
• 5 in the left part of a schematic diagram showing two filter layers which are inserted into a trough-shaped ring and in the right part of a trough-shaped ring having a corrugation in the circumferential direction, which is adapted to the corrugation of the annular filter layers,
• 6 a view of a so-called filter bag, which is formed from a filter layer and which forms the innermost filter layer of the filter body in the radial direction, and
• 7 shows a section along the central axis through the housing of the filter, wherein the individual concentrically arranged filter layers are also shown in section.

Preferred embodiment of the invention

The 1 shows a partial section of a filter body 1 , The filter body 1 is from a plurality of filter layers 2 formed, which are arranged concentrically with each other. The filter layers 2 have a conical shape.

With the arrow 4 is the direction of the through the filter body 1 flowing exhaust gas shown. The outermost filter layer in the radial direction 2 is directly with the housing wall 3 connected in the circumferential direction. Between the filter layers 2 , in particular at the joints between two mutually adjacent filter layers 2 is a circumferentially circumferential sealing element 5 arranged. Such a sealing element is also at the junction between the outermost filter layer 2 and the housing wall 3 arranged.

On the inflow side is also a corrugated spacer 6 between the filter layers arranged. This spacer 6 serves for spacing the mutually adjacent filter layers 2 each other and increasing the stability of the filter body 1 ,

Due to the conical design of the filter layers 2 and the respective alternating arrangement of the filter layers 2 such that the end region of the filter layer 2 is arranged with the smaller diameter alternately towards the inflow side and towards the outflow, the wave-shaped structure of the filter body is formed 1 , In particular, thereby the flow channels 7 formed, which taper from the inflow side to the outflow side, and the flow channels 8th which expand from the inflow side to the outflow side.

The 2 shows in the left part of a section through a joint between two filter layers 2 , wherein the filter layers shown have an area consisting of a metal fleece 9 and an area formed of a fluid-impermeable metal strip 10 , In 2 is in particular the joint between two directly adjacent to each other arranged filter layers 2 shown.

In the left part of the 2 bump the two filter layers 2 directly pointed to each other. They can be soldered together by applying a solder. Alternatively, for example, the roll welding method can be applied to a permanently fluid-tight connection between the two filter layers 2 to create.

In the right part of the 2 is the left filter layer 2 at the joint over the right filter layer 2 worked. In particular, the area formed by the metal strip is 10 over the end area of the right filter layer 2 bent. By this construction, a fluid-tight connection of the filter layers can be achieved in a simple manner, since a double layer is produced in the region of the joint.

The 3 shows a perspective view of an annular filter layer 2 made of a corrugated metal fleece 11 is formed. The filter layer 2 has at the axial end portions in each case a circumferentially extending metal strip 10 on, as he already in 2 was shown. Between the metal strips 10 is a metal fleece 9 arranged, which forms the actual filter material.

The annular filter layer 2 is conically shaped so that the cross section of one axial end portion is smaller than the cross section of the other axial end portion.

4 shows the annular filter layer 2 of the 3 while this on a form element 12 is plugged. The form element 12 has a conically widening from the top cross-section. By pushing on the filter layer 2 on the form element 12 can thus the filter layer 2 obtained a conical shape. The farther the filter layer 2 from the top over the form element 12 is pushed, the more the filter layer is widened. By the different widths pushing on the form element 12 can thus filter layers from identical blanks 2 are formed with different diameters at their respective axial end portions.

The 5 shows in the left part two filter layers 2 again made of a metal fleece 9 and a metal strip 10 formed in a trough-like ring 13 are plugged in. In particular, the metal strips 10 are in the trough-like ring 13 plugged in. To achieve a fluid-tight connection between the filter layers 2 can the filter layers 2 be soldered or welded, for example, with the trough-like ring.

In the right part of the 5 is shown a perspective view of a trough-like ring, the shaping of the corrugated filter layers 2 from the 3 and 4 is adjusted.

The 6 shows a deformed to a bag-shaped structure corrugated filter layer 2 , In this case, in particular, the one axial end region of the filter layer concerned 2 folded in such a way that the metal strip 10 multiple times. The filter layer 2 can be achieved by soldering the contact points between each area of the metal strip 10 be sealed fluid-tight.

This so-called filter bag specifically forms the filter layer located in the center in the radial direction of the filter body.

The 7 shows a section along the central axis 14 through the housing 15 of the filter. In the case 15 are a plurality of concentrically arranged as corrugated, annular elements formed filter layers 16 shown.

The housing 15 is formed by a ring which limits the filter body in the radial direction. The outermost filter layer in the radial direction 16 is at the upper end of the case 15 connected fluid-tight with this, so that no exhaust gas can flow past this filter layer unfiltered through the filter.

The filter layers 16 all have a circumferentially circumferential corrugation, all filter layers 16 has the same number of wave troughs and wave crests except for the innermost layer in the radial direction. The amplitude of the individual waves increases in the radial direction from outside to inside. This is achieved in that preferably all annular filter layers 16 be produced from the same blank. By expanding the annular blanks over a conical shaped element, obtained the filter layers 16 on the one hand their conical shape and on the other hand they get their final diameter. The stronger the filter layers 16 are widened, the stronger the corrugations are flattened.

The outermost filter layer in the radial direction 16 has at least at the junction with the housing 15 virtually no corrugation and thus can be particularly well fluid-tightly connected to the housing.

On average, the 7 It is good to see that the flow channels 17 on the inflow side, which in 7 For example, the top is tapered with increasing inflow. The exhaust gas can be practically along the entire filter layers 16 in the respective filter layer 16 adjacent flow channels 18 overflow. The flow channels 18 increase from the inlet side to the downstream outlet side.

The section through the filter shows the basically zieharmonikaartigen structure of the filter body in the housing 15 , The innermost filter layer in the radial direction is formed into a bag-shaped element and closed on one side in a fluid-tight manner, so that this end region can not be flowed through.

The different features of the individual embodiments can also be combined with each other. The embodiments of the 1 to 6 In particular, they have no restrictive character and serve to clarify the inventive concept.

Claims (18)

Filter for purifying exhaust gases of an internal combustion engine with a housing through which exhaust gas can flow in the axial direction with an inflow side and with an outflow side, wherein in the housing of a plurality of filter layers, a filter body is formed, which can be flowed through by the exhaust gas flow through the housing, characterized characterized in that the filter layers (2, 16) are annular and are arranged concentrically with each other, wherein alternately two radially adjacent mutually adjacent filter layers (2, 16) on the inflow side are fluid-tightly connected to each other and two adjacent to each other in the radial direction filter layers (2, 16) are connected to each other at the outflow side. Filter after Claim 1 , characterized in that the filter body (1) in the radial direction alternately from the inflow side to the outflow side tapered flow channels (7, 17) and from the outflow side to the inflow side tapered flow channels (8, 18). Filter according to one of the preceding claims, characterized in that the filter body (1) in a section along the central axis (14) of the housing (3, 15) has a wavy shape, wherein the corrugation between the inflow side and the outflow side. Filter according to one of the preceding claims, characterized in that the filter layers (2, 16) are formed by a metal fleece (9). Filter according to one of the preceding claims, characterized in that the filter layers (2, 16) on the inlet side facing and / or facing the outflow end portions have a fluid-impermeable extending in the circumferential direction metal strip (10). Filter according to one of the preceding claims, characterized in that the individual filter layers (2, 16) are formed by annularly rolled metal foils, wherein the cross section of the respective filter layers (2, 16) tapers conically or widens conically from the inflow side to the outflow side. Filter according to one of the preceding claims, characterized in that in each case two directly adjacent to one another in the radial direction filter layers (2, 16) are fluid-tightly connected to each other on the inflow side or the outflow side. Filter after Claim 7 , characterized in that the respectively fluid-tightly interconnected filter layers (2, 16) are inserted end in groove-like rings (13) and the respective end portions of the filter layers (2, 16) of the trough-like rings (13) are included. Filter according to one of the preceding claims, characterized in that between two mutually fluid-tightly connected filter layers (2, 16) a circumferentially extending sealing element (5) is arranged. Filter according to one of the preceding claims, characterized in that the radially outermost first filter layer (2, 16) on the inflow side with the housing (3, 15) is fluid-tightly connected in the circumferential direction and this first filter layer (2, 16) on the Outflow side with the radially adjacent to the center directly adjacent second filter layer (2, 16) in the circumferential direction fluid-tight is connected, and the second filter layer (2, 16) on the inflow side with the third filter layer in the radial direction (2, 16) is fluid-tightly connected in the circumferential direction, said this connection principle up to the innermost in the radial direction filter layer (2, 16) continues, the end of the inflow side or the outflow side is fluid-tight with itself closed. Filter according to one of the preceding claims, characterized in that between two mutually in the radial direction directly adjacent filter layers (2, 16) a wave-shaped extending in the circumferential direction of the spacer element (6) is arranged. Filter according to one of the preceding claims, characterized in that the radially innermost filter layer (2, 16) towards the inflow side or towards the outflow end is closed fluid-tight end, whereby this filter layer has a conical basic shape. Filter according to one of the preceding claims, characterized in that the annular filter layers (2, 16) have a corrugation extending in the circumferential direction of the filter body (1). Filter after Claim 13 , characterized in that in the radial direction adjacent to each other filter layers (2, 16) with the exception of the outermost in the radial direction filter layer (2, 16) and the innermost filter layer have the same number of wave crests and troughs in the circumferential direction. Filter after Claim 14 , characterized in that the amplitude of the wave crests and the troughs on the filter layers (2, 16) in the radial direction of the filter body (1) increases from outside to inside. Method for producing a filter according to one of the preceding claims, characterized in that the filter body (1) is formed from a plurality of filter layers (2, 16), which are arranged concentrically to one another and inserted into a housing (3, 15), wherein the individual filter layers (2, 16) are formed by the annular winding of a metal foil and the annular metal foils are then pulled over a conically widening mold element (12), wherein the filter layers (2, 16) forming the filter body (1) from the inside are pulled outwards in each case by a defined distance over the conically widening mold element (12) in order to obtain conical filter layers (2, 16) of increasing diameter. Method according to Claim 16 , characterized in that the annular filter layers (2, 16) have a corrugated shape in the circumferential direction, wherein the amplitude of the corrugation decreases the more, the farther the expansion of the annular filter layers (2, 16) on the mold element (12) Filter layer (2, 16) is pulled over the mold element (12). Method according to one of Claims 16 or 17 , characterized in that the tapered filter layers (2, 16) are interlocked such that the directly adjacent to each other in the radial direction filter layers (2, 16) are arranged alternately with the smaller cross-sectional area to the inflow and outflow, so that a accordion-like structure of the filter body (1) results, wherein the average cross section of the filter layers (2, 16) decreases in the radial direction from outside to inside.

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